1. Field of the Invention
This invention relates to a drawworks. More particularly it relates to a drawworks on a drill floor, the drawworks including an upper pulley assembly connected to a heave-compensated or fixed mounting, and a main block connected to a pipe mount which is laterally movable relative to the drilling centre of the drill floor in at least one direction, the pulley assembly being rotatable about a horizontal first axis perpendicular to the direction of lateral movement.
2. Description of Related Art
A main block belonging to a drawworks on a drill floor is often connected to a drilling machine (top drive) which is arranged to be connectable to a drill string, for example, and which is movable along a vertical rail.
To facilitate the joining or removal of, for example, pipe lengths into/from a drill string, it is also usual for the drilling machine to be laterally movable relative to the drilling centre of the drill floor.
In earlier constructions the pulley axes of the upper pulley assembly and main block were oriented perpendicularly to the direction of lateral movement. Thereby there was no oblique pull on the wire of the drawworks even if the main block was moved sideways.
However, experience went to show that the main block, which is of considerable dimensions, was obstructive to the work on the drill floor when oriented with the pulley axis in said direction. In more recent drawworks the pulley axis of the main block is in the same plane as the direction of lateral movement, whereby the main block takes a position which is, to a considerably degree, less obstructive to the work on the drill floor.
However, when, in its position laterally offset, the main block is hoisted towards its upper position, there is in this more recent construction an unfavourable wire angle between the hoisting wire and the wire pulleys of the upper pulley assembly. This unfavourable wire angle leads to unnecessarily great wear to the pulleys of the upper pulley assembly and to the wire.